Hong Kong (dpa) - Professor Jonathan Sham has an easy method of determining how big a killer colorectal cancer is in a country.

He looks for western-style fast-food chains. If he finds them, then chances are that country will have a growing rate of colorectal cancer, he says.

This is because the existence of fast-food chains is evidence that a country has adopted a western diet and with it the red meat and fats that are known to put people more at risk to colorectal cancer, says Sham, a cancer specialist at the University of Hong Kong.

Throughout the world, colorectal cancer, or bowel cancer, is on the rise with 610,000 new cases in 2008. As a cancer associated with wealth, it was until recently less common in Asia than in the more developed and richer countries.

However, growing affluence and an appetite for western diets in Asian cities has fed a rise in bowel cancer, making it now one of the region's biggest cancer killers.

In Hong Kong, the number of cases has increased by about 3 per cent a year over the last 20 years. It is now the second most common cancer, accounting for 16.4 per cent of all cancer new cases and the second biggest killer, causing 1,686 deaths in 2008.

This alarming trend is echoed in Singapore where it is already the biggest cancer threat, accounting for 6,807 of the 42,000 cancer cases between 2001 and 2005. The same is true in Taiwan where it overtook liver cancer as the most common cancer in 2006.

There are already signs that bowel cancer is gaining a foothold in other Asian countries with cities like Bangkok and Shanghai already having a much higher rate than the rural areas of those countries.

"There has been a dramatic increase in cases of colorectal cancer and basically it's down to modern city living with people eating more meat and animal fat, especially beef, less vegetables and fruit and not doing enough exercise," said Sham.

This factor alone has been seen to be behind the rise in bowel cancer in Japan which witnessed a ten-fold increase in meat consumption between the 1950s and 1990s.

The risk also increases with people who smoke and drink, and with age with about 90 per cent of cases occurring in people over age 50. This is another reason why countries like Hong Kong with its growing population of elderly are seeing a rise in bowel cancer.

Up to 20 per cent of bowel cancer cases are due to a mutated gene, while the remaining 80 per cent are said to be sporadic and as a result are more likely to go undetected in the earlier stages when they have a better chance of being successfully treated.

According to Sham, in most cases symptoms such as changes in bowel habits only occur when the cancer is advanced which means around 50 to 60 per cent of all cases result in death.

Studies have shown that bowel cancer occurs predominately as a result of cell abnormalities in the colon which start as small growths called polyps. The majority are harmless, but if left untreated a very small percentage can become cancerous.

However, this transition normally takes place over around ten years and it is this timescale which works to our advantage, making it a preventable cancer, says Dr Yuen Siu-tsan, a medical advisor to the Hong Kong Cancer Fund.

Prevention is possible through regular screening called a colonoscopy or sigmoidoscopy. This involves passing a flexible tube with a camera through the whole or part of the colon via the rectum. This allow the doctor to look for and remove the polyps before they develop into cancer.

"We know that most tumours pass through a stage as a polyp before they become tumours. So if an individual has regular colonoscopy and removal of polyps whenever they appear, then in theory they can prevent colorectal cancer," said Sham.

Sham and fellow experts recommend people undergo a colonoscopy once every ten years from the age of 50.

However, in Hong Kong, as in many countries, the government does not pay for screening unless patients already have symptoms or have a family history of this particular cancer.

The cost to go private ranges from around 500 to 1,000 US dollars but Yuen believes in the light of the growing threat of bowel cancer, it's a cost which people should be willing to bear.

"You need a colonoscopy once every ten years. If you divide the cost by 10 years then protection from cancer will only cost you the price of a night out every year. I consider that money well spent."